Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $62.78   7.766%   $67.6555   $67.66   $67.65   $67.70  
  Purchase #2 $248.82   3.724%   $258.0861   $258.09   $258.10   $258.10  
  Purchase #3 $115.43   8.546%   $125.2946   $125.29   $125.30   $125.30  
  Purchase #4 $235.92   5.698%   $249.3627   $249.36   $249.35   $249.40  
  Purchase #5 $134.25   9.293%   $146.7259   $146.73   $146.75   $146.70  
  Purchase #6 $154.99   3.537%   $160.472   $160.47   $160.45   $160.50  
  Purchase #7 $65.68   5.622%   $69.3725   $69.37   $69.35   $69.40  
  7 purchase totals = $1,017.87       $1,076.9693   $1,076.97   $1,076.95   $1,077.10